Sensitivity Monitoring of the SECCHI COR1 Telescopes on STEREO
Measurements of bright stars passing through the fields of view of the inner coronagraphs (COR1) on board the Solar Terrestrial Relations Observatory (STEREO) are used to monitor changes in the radiometric calibration over the course of the mission. Annual decline rates are found to be \(0.648 \pm 0.066\)%/year for COR1-A on STEREO Ahead and \(0.258 \pm 0.060\)%/year for COR1-B on STEREO Behind. These rates are consistent with decline rates found for other space-based coronagraphs in similar radiation environments. The theorized cause for the decline in sensitivity is darkening of the lenses and other optical elements due to exposure to high-energy solar particles and photons, although other causes are also possible. The total decline in the COR-B sensitivity when contact with Behind was lost on 1 October 2014 was 1.7%, while COR1-A was down by 4.4%. As of 1 November 2017, the COR1-A decline is estimated to be 6.4%. The SECCHI calibration routines will be updated to take these COR1 decline rates into account.
The author would like to thank Chris St. Cyr for several helpful suggestions, and Nathan Rich for help with the thermal history. The author would also like to thank the anonymous referee for several helpful suggestions. This work was funded under NASA Contract NNG06EB68C. The STEREO/SECCHI data used here are produced by an international consortium of the Naval Research Laboratory (USA), Lockheed Martin Solar and Astrophysics Lab (USA), NASA Goddard Space Flight Center (USA) Rutherford Appleton Laboratory (UK), University of Birmingham (UK), Max-Planck-Institut für Sonnensystemforschung (Germany), Centre Spatiale de Liége (Belgium), Institut d’Optique Théorique et Appliquée (France), and Institut d’Astrophysique Spatiale (France).
Disclosure of Potential Conflicts of Interest
The author declares that he has no conflicts of interest.
- Ducati, J.R.: 2002, VizieR online data catalog: catalogue of stellar photometry in Johnson’s 11-color system. VizieR Online Data Catalog 2237. ADS.
- Howard, R.A., Moses, J.D., Vourlidas, A., Newmark, J.S., Socker, D.G., Plunkett, S.P., Korendyke, C.M., Cook, J.W., Hurley, A., Davila, J.M., Thompson, W.T., Cyr, O.C.S., Mentzell, E., Mehalick, K., Lemen, J.R., Wuelser, J.P., Duncan, D.W., Tarbell, T.D., Wolfson, C.J., Moore, A., Harrison, R.A., Waltham, N.R., Lang, J., Davis, C.J., Eyles, C.J., Mapson-Menard, H., Simnett, G.M., Halain, J.P., Defise, J.M., Mazy, E., Rochus, P., Mercier, R., Ravet, M.F., Delmotte, F., Auchere, F., Delaboudiniere, J.P., Bothmer, V., Deutsch, W., Wang, D., Rich, N., Cooper, S., Stephens, V., Maahs, G., Baugh, R., Mcmullin, D.: 2008, Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI). Space Sci. Rev. 136, 67. DOI. ADS. ADSCrossRefGoogle Scholar
- von Rosenvinge, T.T., Reames, D.V., Baker, R., Hawk, J., Nolan, J.T., Ryan, L., Shuman, S., Wortman, K.A., Mewaldt, R.A., Cummings, A.C., Cook, W.R., Labrador, A.W., Leske, R.A., Wiedenbeck, M.E.: 2008, The High Energy Telescope for STEREO. Space Sci. Rev. 136, 391. DOI. ADS. ADSCrossRefGoogle Scholar